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Income Taxes (Deferred) (Details) - CAD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Components of Deferred Tax Assets [Abstract] |  |
Deferred Tax Assets, Tax Loss Carry Forwards | $ 917 | $ 853
Tax credit carry forwards | 269 | 314
Regulatory liabilities - cost of removal | 206 | 208
Deferred Tax Assets, Derivative Instruments | 90 | 107
Pension and post-retirement liabilities | 126 | 112
Deferred Tax Assets, Other | 441 | 394
Deferred Tax Assets, Gross, Total | 2,049 | 1,988
Deferred Tax Assets, Valuation Allowance | (163) | (105)
Deferred Tax Assets, Net of Valuation Allowance, Total | 1,886 | 1,883
Components of Deferred Tax Liabilities [Abstract] |  |
Deferred Tax Liabilities, Property, Plant and Equipment | (2,591) | (2,321)
Deferred Tax Liabilities, Derivatives | (124) | (155)
Deferred Tax Liabilities, Other | (316) | (292)
Deferred Tax Liabilities, Gross, Total | (3,031) | (2,768)
Noncurrent Deferred Tax Liabilities And Assets [Abstract] |  |
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent | 175 | 138
Deferred Tax Liabilities, Net, Noncurrent | (1,320) | (1,023)
Deferred Tax Assets (Liabilities), Net, Noncurrent, Total | $ (1,145) | $ (885)

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- Definition Amount of deferred tax liability attributable to taxable temporary differences. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(15)(b)(2)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(15)(2)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(26)(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(26)(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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